Distribution and storage of electricity are critical aspects of modern infrastructure. Power distribution includes the transmission of power at high voltage. Once power is generated it is conditioned and transformed for transmission to remote users of power. As these high current and voltage power sources reach their destinations, they must be adjusted to the needs of the loads that will use them, whether that be residential or commercial standards, or more esoteric industrial loads. Transformers are critical component in these systems for adjusting the voltage between generation, distribution, and use of electrical power. Like all electrical equipment, transformers and the systems of which they are a part require periodic service.
Many transformers include an oil switch that must be toggled or rotated to the off position before the transformer can safely be serviced. For example, any enclosed pad mount transformers with an oil switch in the terminal cabinet will require manipulation of the oil switch before service. Unfortunately, this oil switch is often disposed within the transformer housing, located within the transformer terminal cabinet. Because this internal area of the transformer also includes active high-voltage components, it is a significant risk to the technician servicing the transformer to open the housing and access the oil switch.
In order to service a transformer with an internal oil switch, the technician must first open an access panel, generally a hinged and lockable door, that provides access to the transformer terminal cabinet within the transformer housing. Among the active electrical components in the transformer terminal cabinet, is a rotary oil switch that is rotated to be able to safely power down the transformer for service. The rotary oil switch is then turned by hand or using an electrical service hot stick with a hooked end to engage a loop or other feature on the oil switch. Once the switch is fully in the off position, service on the transformer unit can proceed.
Accidental contact with the active electrical components within the transformer cabinet is extremely dangerous to the technician and can result in fatal injury. Danger may be particularly high in older equipment where safety features, such as insulation, of the exposed electrical components have degraded. While service technicians are highly trained in understanding these risks, routine exposure tends to reduce their safety mindedness. Once a hand is within the cabinet in the vicinity of the exposed electrical components, any number of circumstances can cause accidental contact with active electrical components and resulting injury or death.
While transformer cabinets could be designed with a safety switch in a separate access panel, that is not the standard configuration. Even if this change was made in the industry, there would still be the vast installed base of transformers that do not include such a feature and will need to be safely serviced for many years to come.